One method for measuring the concentration of a specific component in a sample liquid is a method in which the specific component concentration is computed from the potential difference arising when a reference liquid containing a known concentration of the specific component and a sample liquid containing an unknown concentration of the specific component are electrically shunted.
In this method, by for example setting a plate for concentration measurement relative to the analyzer, the concentration of the specific component is measured. Below, the case in which the concentrations of three types of specific components (for example, K+, Na+, Cl−) in a sample liquid are measured is explained.
The analyzer has, at least, a set portion in which a plate for concentration measurement is set; three pairs of probes (for a total of six); and computation means to compute the concentration of the specific component from the potential differences between each pair of probes.
The plate for concentration measurement has, at least, a reference liquid reception portion, onto which reference liquid is spot-applied; a reference liquid holding portion, which holds the reference liquid; first through third terminal portions, which are in electrical contact with the reference liquid of the reference liquid holding portion; a sample liquid reception portion, into which the sample liquid is spot-applied; a sample liquid holding portion, which holds the sample liquid; fourth through sixth terminal portions, which are in electrical contact with the sample liquid holding portion; and a bridge, which electrically shunts the reference liquid of the reference liquid holding portion and the sample liquid of the sample liquid holding portion.
When the concentration measurement plate is set in the set area of the analyzer, the corresponding probe of the analyzer is in contact with each of the terminal portions. In the analyzer, potential differences between the reference liquid and sample liquid are measured for each specific component, via each probe pair. The computation means of the analyzer computes the concentrations of each specific component based on the potential difference measurement results.
In this analyzer, instead of a concentration measurement plate, a check plate is set in the set portion, and the potential difference measurement electrical circuit is tested for defects. Causes of electrical circuit defects include, for example, malfunctions of electronic parts, breakage in wiring, and contact failure between a probe and the concentration measurement plate (first through sixth terminal portion).
A method of test of the electrical circuit for potential difference measurement is described in, for example, JP-B 6-82113 and in JP-B 7-111409.
The test method described in JP-B 6-82113 employs check plates 9A to 9D, as shown in FIGS. 15 to 18 of this application. Each of these check plates 9A to 9D has a base plate 90 in which are provided a total of six through-holes 90a corresponding to three pairs of probes in the analyzer. On the base plate 90 is stacked a cover plate 92, enclosing conducting layers 91a to 91d. Various configurations for the conducting layers 91a to 91d are shown in FIGS. 15 to 18.
Each of these check plates 9A to 9D is set in the analyzer similarly to a test plate. At this time, each of the probes is in contact with the conducting layers 91a to 91d, so that each of the probe pairs is shunted. Test of the electrical circuit for potential difference measurement is performed by measuring the potential differences between the probe pairs. In this test method, if the potential difference between each probe pair is zero, the electrical circuit for potential difference measurement of the analyzer is judged to be normal, and if not zero, the circuit is judged to be abnormal.
In this test method, measured potentials are always zero, so that it is not possible to test reliably for the presence of defects in the electrical circuit for potential difference measurement. For example, even in a case in which a measurement value corresponding to the actual potential difference cannot be observed due to some abnormality, the measured value for the zero potential in tests is measured as either zero or as a value close to zero. In this case, it is judged that there is no abnormality in the electrical circuit for potential difference measurements. It is also difficult to determine the measurement precision for potentials which deviate greatly from zero potential.
On the other hand, in the test method described in JP-B 7-111409, a check plate 9E such as shown in FIG. 19 is used. This check plate 9E has a base plate 90 in which are provided a total of six through-holes 90a corresponding to the three probe pairs of the analyzer. On this base plate 90 are placed six conducting pads 91e which separately cover each of the through-holes 90a. These conducting pads 91e, together with resistors R1 to R3 and a battery 91f, constitute an electrical circuit as shown in FIG. 20. The conducting pads 91e, resistors R1 to R3, and battery 91f are enclosed by the frame 92 positioned on the base plate 90. The space enclosed by the frame 92 is sealed with resin.
With the probes brought into contact with the conducting pads 91e in the check plate 9E, a voltage is applied across each of the probe pairs by the battery 91f. The voltage value for each probe pair is measured, and the electrical circuit for potential difference measurement is tested for defects.
In this test method, a voltage is applied to each of the probe pairs by the battery 91f incorporated into the check plate 9E, so that the precision of the output of the battery 91f necessarily has an effect on the test results. The battery output is not strictly constant; in particular, if consumption exceeds a certain capacity, the output gradually declines. Hence a method which employs a battery 91f cannot be regarded as appropriate in order to maintain test precision. Moreover, it is difficult to make the output of the battery 91f incorporated into the check plate 9E variable. Consequently a given check plate 9E can only perform tests using a single reference potential, and so there is the drawback that, similarly to test methods described in the previous publications, defects in an electrical circuit for potential difference measurement cannot be reliably detected.